Estimates of the total number of living species on Earth are still very approximate, ranging from a few million to tens of millions. Much of the uncertainty arises from patchy collecting, especially in the tropical oceans. In an intensive collecting program around New Caledonia in the western Pacific Ocean, Bouchet et al. recorded nearly 3000 mollusk species—more than twice as many as have been previously recorded from comparable areas. Most of these species were recorded from fewer than six of 42 collecting stations in the 295 km2 study area, indicating the importance of relatively rare species in contributing to total biodiversity. It is still impossible to extrapolate from these figures to estimate total mollusk species richness in the tropical oceans to within less than an order of magnitude. Nevertheless, because mollusks contribute more than 50% of the total invertebrate species in the tropical Indo-Pacific waters, it is clear that total marine species richness is likely to be revised upward as further intensive collections are made.—AMS